The RGD tripeptide sequence is found in a number of proteins, where it plays a role in cell adhesion. Examples of proteins in which the RGD tripeptide sequence is present include collagens, fibronectin, vitronectin, von Willebrand factor (VWF), certain disintegrins, and certain discoidins.
Integrins are heterodimeric cell surface receptors which mediate adhesion between cells and the extracellular matrix (ECM) by binding to ligands having an exposed RGD sequence. Normal integrin-RGD binding is believed to play a role in gene expression involved in cell growth, migration, and survival. Faulty regulation of such cell growth, migration, and survival can result in a number of disease states including thrombosis, inflammation, and cancer. Thus, RGD peptides have been investigated as potential mimics of cell adhesion proteins and for their ability to bind to integrins for therapeutic purposes such as inhibiting cell adhesion, cell migration, cell proliferation, cell differentiation, apoptosis, angiogenesis, tumorigenesis, for inhibiting entry of microbes into cells, for the use in their multimeric form as internal radiotherapeutic agents as well as cancer imaging agents and for their anti-cancer drug carrying abilities.
In the eye, integrins affect a number of processes including ocular development, cell migration, healing and some pathologic processes. Integrins may also modulate inflammation and thrombosis in ocular tissue. Intravitreally injected RGD peptide has also been reported to cause posterior vitreoretinal detachment in an animal model and, thus, may be useful in the treatment of certain retinal disorders and/or to facilitate removal of the vitreous body in a vitrectomy procedure. See Olivera, L. B., et al., RGD Peptide-Assisted Vitrectomy to Facilitate Induction of a Posterior Vitreous Detachment: a New Principle in Pharmacological Vitreolysis; Current Eye Research (8):333-40 (Dec. 25, 2002).
Integrins are also known to be used by various enveloped and non-enveloped viruses and bacteria in infecting host cells. Schornberg, Kathryn L.; α5β1-Integrin Controls Ebolavirus Entry by Regulating Endosomal Cathespins; Proc. Nat. Acad. Sci. USA; Vol. 106, No. 19, pp. 8003-8008 (2009)